If they offered both (monthly and one-time payments) then the solution would be to allow the project to allow only one or the other or both or neither. So you could select that you'd only receive monthly payments and people wouldn't be able to send you one-time payments.
Even better (imo), try to buffer one time payments over months. This (and other similar features) could allow a developer to see upcoming income from OSS, if it's declining, etc.
Being able to predict how much you're going to make it hugely helpful imo. Especially if you're a freelancer. You might see that in 3 months your funds are drying up, so plan accordingly.
Just brainstorming: But "similar features" could be trying to favor longer term donations. If a user wants to donate $20/m, maybe ask them for $10/m for 3 month increments?
Though, I suppose this isn't any better than the developer themself buffering funds in their bank. BUT, it seems like a meaningful concept, regardless.
